The present invention relates to an image processor in a color electrophotographic printer for reproducing an image utilizing plural colors of toner such as a color printer and a color copying machine and an image processing method used by the same, particularly image processing that enables optimum color processing according to the type of an object and further, arbitrary color processing every predetermined print unit which is smaller than an object.
An image processor in a color electrophotographic printer such as a color printer interprets print data, writes the RGB color data for every dot to a band memory which is an image memory, executes color conversion including specified color correction processing for RGB color data in the band memory, generates the color data of yellow, magenta, cyan and black (YMCK) and executes halftoning processing for applying halftone representation by halftone dots composed of plural dots to the above data. In this specification, color conversion and halftoning processing are called color processing altogether. Image reproduction data generated as a result of color processing is supplied to a printer engine and an image is reproduced on predetermined printing paper.
As for the above color processing, optimum color correction and halftoning processing are different depending upon a printed object image. There is also a case that color correction and halftoning processing are specified in an arbitrary print unit by a creator of images independent of an object image. For example, in the case of an image including many relatively thin lines where the natural change of gradation is small such as a character and a graph, it is desired that the screen ruling is increased possibly to obtain a fine halftone dot and to prevent a void from being made in a character and a line. It is also desired that in color conversion from the color space of RGB to the color space of YMCK, brightness is enhanced possibly, though current color is different from original color without color matching by mixing toner which causes the deterioration of saturation.
On the other hand, in the case of an image in which the natural change of gradation is included in relatively large area such as a picture image, it is desired that the screen ruling is reduced possibly to obtain a coarse halftone dot and to prevent a banding caused by jitter in paper feed from being emphasized and in color conversion, color correction including color matching for matching with original color is made to faithfully reproduce the natural change of gradation in an image.
Heretofore, it is proposed that an identifier for identifying an object in print data is recorded every pixel and color processing according to the identifier is executed. For example, there is disclosed in Japanese Patent Publication No. 10-51653A. Hereby, in color processing, color correction according to an identifier every pixel and binarization processing are executed.
However, in conventional type image processing, a few numbers of color processing set beforehand for every object is merely selected suitably and processed. If color processing is automatically selected depending upon an object or color processing is arbitrarily selected by the creator of images, many color correction tables and many halftoning processing tables respectively used for color processing are required to be provided in a memory. As a result, a problem that hardware composing a color processing section becomes enormous and particularly, a rapid access memory for storing the above tables requires large capacity occurs.
A creator of images may make color coordination such as color enhancement for every arbitrary print unit and the provision of color processing which can flexibly correspond to such color coordination is desired.